Novel interactions between NK cells and B lymphocytes have been recently uncovered in our laboratory. The addition of NK cells to resting B lymphocytes in the presence of lymphokines results in B cell activation and immunoglobulin secretion. -On the other hand, the interaction between NK cells and in vivo activated B lymphocytes results in the stimulation of tauIFN production by NK cells which in turn causes the preferential synthesis of IgG2a. These results support recent findings in other laboratories which suggest that NK cells can regulate immune responses in manners other than via cytolysis. it is the goal of this project to first continue efforts to fully characterize the nature of the interaction between NK cells and B cell subpopulations and to assess whether this interaction involves different subsets of NK cells than those involved in target cell lysis. To this end, the molecular mechanisms underlying the induction of tauIFN mRNA production when NK cells are activated by different means will be also determined. Finally, and most importantly, the physiological significance of these interactions will be explored by adoptive transfer experiments by which the interacting subpopulations can be manipulated in vivo. These studies should contribute significantly towards the understanding of the role of NK cells in the regulation of B lymphocytes responses in particular as well as provide some insights regarding the regulatory role of NK cells in general.